Coated activated carbon for contaminant removal from a fluid stream

ABSTRACT

Product attrition by dusting of granular and shaped activated carbons is disclosed to be reduced significantly, or essentially eliminated, by the application of a thin, continuous polymer coating on the granular or shaped activated carbon, without a reduction in adsorption velocity or capacity of the activated carbon when used in fluid stream filters for removing contaminants. The avoidance of carbon dust leads to improved fluid stream filter performance in contaminant removal.

[0001] This application is a continuation-in-part application of Ser.No. 09/448,934 titled “Coated Activated Carbon,” by L. H. Hiltzik, E. D.Tolles, and D. R. B. Walker, filed on Nov. 23, 1999.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to activated carbon pellets and activatedgranules with improved dusting characteristics for contaminant removalfrom water. In particular, this invention relates to activated carbonssusceptible to dust attrition due to abrasion where dusting can resultin loss of product and often cause other problems related to its use incontaminant removal from drinking water.

[0004] 2. Description of Related Art (Including Information DisclosedUnder 37 CFR 1.97 and 37 CFR 1.98

[0005] Active carbon long has been used for removal of impurities andrecovery of useful substances from liquid and gas fluid streams becauseof its high adsorptive capacity. Generally, “activation” refers to anyof the various processes by which the pore structure is enhanced.Typical commercial activated carbon products exhibit a surface area (asmeasured by nitrogen adsorption as used in the B.E.T. model) of at least300 m²/g. For the purposes of this disclosure, the terms “active carbon”and “activated carbon” are used interchangeably. Typical activationprocesses involve treatment of carbon sources, such as resin wastes,coal, coal coke, petroleum coke, lignites, polymeric materials, andlignocellulosic materials including pulp and paper, residues from pulpproduction, wood (like wood chips, sawdust, and wood flour), nut shell(like almond shell and coconut shell), kernel, and fruit pits (likeolive and cherry stones) either thermally (with an oxidizing gas) orchemically (usually with phosphoric acid or metal salts, such as zincchloride).

[0006] Chemical activation of wood-based carbon with phosphoric acid(H₃PO₄) is disclosed in U.S. Pat. No. Re. 31,093 to improve the carbon'sdecolorizing and gas adsorbing abilities. Also, U.S. Pat. No. 5,162,286teaches phosphoric acid activation of wood-based material which isparticularly dense and which contains a relatively high (30%) lignincontent, such as nut shell, fruit stone, and kernel. Phosphoric acidactivation of lignocellulose material also is taught in U.S. Pat. No.5,204,310 as a step in preparing carbons of high activity and highdensity.

[0007] Also, U.S. Pat. No. 4,769,359 teaches producing active carbon bytreating coal cokes and chars, brown coals or lignites with a mixture ofNaOH and KOH and heating to at least 500EC in and inert atmosphere. U.S.Pat. No. 5,102,855 discloses making high surface area activated carbonby treating newspapers and cotton linters with phosphoric acid orammonium phosphate. Coal-type pitch is used as a precursor to prepareactive carbon by treating with NaOH and/or KOH in U.S. Pat. No.5,143,889.

[0008] Once the activated carbon product is prepared, however, it may besubject to some degradation before and during its use. Abrading duringmaterials handling and actual use of such activated carbon results inloss of material in the form of dust. Such “dusting” of the product is afunction of its relative hardness and its shape, as well as how it ishandled in the plant-in moving it into and out of plant inventory, inloading for transport and in off-loading by the receiver, and in how itis handled by the receiver to place the product into use. In certainapplications, where the activated carbon is subject to constantvibration or erosion, product degradation by dusting continues throughthe life of the product.

[0009] The hardness of an activated carbon material is primarily afunction of the hardness of the precursor material, such as a typicalcoal-based activated carbon being harder than a typical wood-basedactivated carbon. The shape of granular activated carbon also is afunction of the shape of the precursor material. The irregularity ofshape of granular activated carbon, i.e., the availability of multiplesharp edges and corners, contributes to the dusting problem. Of course,relative hardness and shape of the activated carbon are both subject tomodification. For example, U.S. Pat. Nos. 4,677,086, 5,324,703, and5,538,932 teach methods for making pelleted products of high densityfrom lignocellulosic precursors. Also, U.S. Pat. No. 5,039,651 teaches amethod of producing shaped activated carbon from cellulosic and starchprecursors in the form of “tablets, plates, pellets, briquettes, or thelike.” Further, U.S. Pat. No. 4,221,695 discloses making an “Adsorbentfor Artificial Organs” in the form of beads by mixing and dissolvingpetroleum pitch with an aromatic compound and a polymer or copolymer ofa chain hydrocarbon, dispersing the resultant mixture in water givingrise to beads, and subjecting these beads to a series of treatments ofremoving of the aromatic hydrocarbon, infusibilizing, carbonizing, andfinally activating.

[0010] Despite these and other methods of affecting activated carbonhardness and shape, however, product dusting continues to be a problemin certain applications. For example, in U.S. Pat. No. 4,221,695, notedabove, the patentees describe conventional beads of a petroleumpitch-based activated carbon intended for use as the adsorbent inartificial organs through which the blood is directly infused that arenot perfectly free from carbon dust. They observe that some dust stealsits way into the materials in the course of the preparation of theactivated carbon, and some dust forms when molded beads are subjected towashing and other treatments. The patentees reflected conventionalwisdom in noting that the application of a film-forming substance to thesurface of the adsorbent “is nothing to be desired,” because the appliedsubstance acts to reduce the adsorption velocity of the matters to beadsorbed on the adsorbent and limit the molecular size of such mattersbeing adsorbed.

[0011] Subsequently, however, in U.S. Pat. No. 4,476,169, the patenteesdescribe a multi-layer glass window wherein vapor between the glasssheets is adsorbed by a combination of a granular zeolite with granularactivated carbon having its surface coated with 1-20 wt % syntheticresin latex. The coating of the activated carbon is described as greatlyinhibiting the occurrence of dust without substantially reducing theabsorptive power of activated carbon for an organic solvent.

[0012] The present invention relates to the discovery that activatedcarbon, granular or pelletized, can be coated to reduce dust that is anuisance in contaminant removal from fluid streams, and particularly inpoint-of-use (POU) water treatment applications. A coating can beapplied that causes no significant decrease in performance for POU waterfilter applications, as measured by chlorine removal performance.Additionally, activated carbon can be colored by applying pigment andbinder to either coated or uncoated activated carbon. Insolublepigments, rather than soluble dyes, are preferred since soluble dyes areadsorbed by activated carbon yielding a black product that leaches colorafterwards as the dye desorbs. Colored coatings may also be used toprovide a functional indicator to show when a carbon filter is spent.Colored coatings can be applied for aesthetic purposes, such as forcarafe type filters, so that the activated carbon is not black.Different colors can provide an effective means of differentiatingbetween different activated carbon grades, such as grades for chlorineremoval and grades for chlorinamine removal. Also, color can be used toidentify the year of manufacture, quality assurance, and/or brandidentification. For example, a water filter manufacturer could demand ared activated carbon filter media to assure that some othermanufacturer's activated carbon is not used in its place.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a graphical representation of the initial dust values ofpolymer coated, shaped activated carbons of various sources, as well asthe effect of the polymer coating on their respective initial dustvalues, as reported in Table III.

[0014]FIG. 2 is a graphical representation of the dust rate values ofpolymer coated, shaped activated carbons of various sources, as well asthe effect of the polymer coating on their respective dust rate values,as reported in Table III.

[0015]FIG. 3 is a graphical representation of the fines content as afunction of polyethylene coating content

[0016]FIG. 4 is a graphical representation of chlorine removal by 2%polyethylene coated and uncoated 10×20 mesh activated carbon.

SUMMARY OF THE INVENTION

[0017] It has been discovered that product attrition by dusting ofgranular and shaped activated carbons can, in fact, be reducedsignificantly, or essentially eliminated, by the application of a thin,continuous polymer coating on the granular or shaped activated carbon,without a reduction in adsorption velocity or capacity of the activatedPOU carbon contaminant removal filters. The avoidance of attrited carbondust leads to improved chlorine removal performance in water filtration.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0018] Manufacturers of filters used to remove contaminants from fluidstreams often direct users to flush carbon filters of dust before afilter is put into service. Dust issues have led some manufacturers touse carbon blocks instead of granular carbon. Ideally, a coated carbonwould not require flushing and would have the same adsorptive and/orremoval performance as an uncoated carbon. Filter manufacturers may evenaccept a slight reduction in performance in exchange for reduction ofdust. Chlorine removal (from water) testing shows that significant dustreduction is possible with little to no loss in chlorine removalefficacy.

[0019] A method is disclosed based on applying a visible polymer coatingon the finished product and then removing any residual dust. The productis considered dust free, as shown by an “initial dust” value of ≦0.3mg/dL and a “dust rate” value of ≦0.01 mg/min/dL, both below thedetection limits of the standard dust attrition test. The product is“essentially” dust free, as shown by a “dust rate” value of ≦0.06mg/min/dL, a detectable value but dramatically lower than the dust rateof uncoated activated carbon and, as noted in the tables which follow inthe examples below, is the highest dust rate value of theinvention-treated activated carbons. The retention of butane adsorptionand working capacity properties are an important feature of the coatedpellets. As shown in the examples below, the coated pellets retained94-100% of the uncoated pellet butane activity and 88-100% of theuncoated pellet butane working capacity (BWC). For example, theinvention coated shaped and granular activated carbon will have a butaneactivity of greater than 15 g/100 g, preferably greater than 25 g/100 g,more preferably greater than 35 g/100 g, even more preferably greaterthan 45 g/100 g, even more preferably greater than 55 g/100 g, even morepreferably greater than 65 g/100 g, and most preferably greater than 75g/100 g. Also, the invention coated shaped and granular activated carbonwill have a butane working capacity greater than 9.0 g/dL, preferablygreater than 10.0 g/dL, more preferably greater than 11.0 g/dL, evenmore preferably greater than 12.0 g/dL, even more preferably greaterthan 13.0 g/dL, even more preferably greater than 14.0 g/dL, and mostpreferably greater than 15.0 g/dL.

[0020] An additional feature is that this coating provides the pelletswith a glossy and attractive appearance that calls attention to productcleanliness. The glossy nature of the coating results from thefilm-forming nature of the polymer and the emulsion form by which it isapplied to the pellets. An added facility, and possible benefit,provided by the invention composition and process is achieved by thenatural color of the coating material or by the addition of coloringagents, such as pigments and optical brighteners, to the polymeremulsion. In particular, distinct carbon products may be identifiedthrough color-coding. The color-coding may relate to productapplication, plant origination, customer designation, or any designationdesired.

[0021] The difference in appearance between the invention emulsioncoated glossy pellets and previous dispersion-coated pellets is due tothe different forms of the polymers used in applying the coatings. Theparticle sizes of emulsions are smaller than dispersions, thereforeemulsions form continuous films due to the effects of capillary forceswhen dried of the carrier liquid. Dispersions do not form continuousfilms by drying, and they leave behind discrete (i.e., noncontinuous)polymer particles similar in size to the originally dispersed particles.The continuous, emulsion-applied polymer film, on the other hand,provides a glossy appearance, coating integrity, pellet dust reduction,and hydrophobicity that a dispersion-applied, non-continuous film doesnot.

[0022] Also, it should be noted that while the polymer film resultingfrom the application of the polymer emulsion onto the shaped or granularcarbon is a continuous film, it may be porous or non-porous, dependingon the irregularity of surface shape of the carbon material. Theappearance of a porous continuous film occurs more often on the moreirregular shaped granular activated carbons than on shaped activatedcarbons.

[0023] A variety of colored carbons can be prepared by choosing theproper combination of pigments for addition to the polymer emulsion andthe emulsion application methods, as taught in the foregoing examples,in order to attain the desired color, plus obtain the desired benefitsof the coating.

[0024] The process for essentially eliminating dust attrition ofactivated carbon material by coating the activated carbon materialcomprising the steps of:

[0025] (a) spraying an emulsion of the polymer onto exposed surfaces ofthe activated carbon material while it is in a state of turbulence at aprocessing temperature above ambient temperature; and

[0026] (b) drying the coated activated carbon material.

[0027] The process may optionally include an initial step of preheatingthe active carbon material to above ambient temperature. The process mayinclude multiple repetitions of steps (a) and (b). Also, the process ofthe claimed invention may comprise a further step

[0028] (c) de-dusting the dried coated activated carbon material byremoving any residual dust therefrom.

[0029] As those skilled in the art appreciate, various processingconditions are generally interdependent, such as processing time andprocessing temperature. These operating conditions as well may depend onthe nature of the carbon material to be coated (shaped or granular,coal-based or lignocellulosic-based, etc.) and the coating material(relative volatility, viscosity, etc.). Thus, the temperature range forcoating application and coating drying steps may range from just belowambient of about 50° F., up to about 280° F. (138° C.), and theprocessing time may take from about 1 minute to about 12 hours. For mostcombinations of shaped or granular active carbon material and coatingmaterial, a preferred operating temperature range for the coating anddrying steps is from about 70° F. (21° C.) to about 250° F. (121° C.)for from about 5 minutes to about 6 hours.

[0030] The turbulent state of the active carbon material can be inducedby various known means. For example, the carbon material, in granular orshaped (usually pellet) form, may be placed in a rotary tumbler, in amixing device, or on a fluidized bed. While it is critical that theactive carbon material be in a kinetic, rather than static, state whenthe coating material is applied to assure relative even coating on thesurface area of the active carbon material, it is not critical how thekinetic state is achieved.

[0031] The coating materials useful in the claimed invention are thosecapable of forming a continuous film. In particular, polymers,copolymers, and polymer blends that are suitable coating materialsinclude: polyolefins, such as polyethylene, polypropylene,polyisobutylene, polystyrene, polyisoprene, polychloroprene,poly-4-methyl-1-pentene, polybutadiene, and polybutene; polyacrylics,such as polyacrylates, polymethyl methacrylate, polybutylmethacrylate,polymethacrylates, and polyacrylic acid; halogen-substituted alkanes,such as polytetrafluoroethylene, trifluoroethylene, vinyl fluoride,fluorvinylidene, fluorobutylene, and fluoropropylene; and other polymersincluding polyurethane, polyethylene terephthalate, styrene butadiene,modified polybutadiene, epoxies, modified alkyds, polyesters, starches,methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinylacetate, cellulose acetate, cellulose nitrate, cellulose tri acetate,cellulose acetate, phthalate, cellulose propionate morpholinobutyrate,hydroxypropylmethyl cellulose, ethylene vinyl acetate, acryliccopolymers, polysulfones, polyether sulfones, polyethers, polyethylene,glycols, polyimines, polybutylene, polyvinyl ethers, polyvinyl esters,polyalkylsulfides, polyarylsulfides, lignosulfonates, polyacrylamide,cyanoacryl ate, polyamides, polyimides, polysiloxanes,methacrylonitrile, polyacrylonitrile, polyvinyl pyridine, polyvinylbenzene, polyvinyl acetate, polyvinyl pyrrolidene, polyvinyl butyral,polyvinyl alcohol, polyvinyl chloride, polyvinyl formaldehyde,polyformaldehyde, polycarbonates, and polyvinylidene chloride.

[0032] The shaped or granular active carbon material of the inventiondescribed herein may be derived from any known active carbon precursorsincluding coal, lignocellulosic materials, including pulp and paper,residues from pulp production, wood (like wood chips, sawdust, and woodflour), nut shell (like almond shell and coconut shell), kernel, andfruit pits (like olive and cherry stones), petroleum, bone, and blood.

[0033] Gas and vapor phase streams of commercial importance that can betreated with activated carbon include: air, helium, neon, argon,krypton, xenon, hydrogen, oxygen, nitrogen, methane, natural gas,ethane, ethylene, propane, propylene, carbon dioxide, syngas, carbonmonoxide, ammonia, chlorofluorocarbons, chlorofluorohydrocarbons, sulfurhexafluoride and vapor spaces in contact with volatile organiccompounds, such as fuel tanks of all sizes.

[0034] Liquid streams of commercial importance that are treated withactivated carbon include: process water, drinking water, solutions ofsugars or carbohydrates such as high fructose corn syrup, solutionsobtained during the processing of sugar cane and sugar beets, fruitjuices, wine, beer, malt beverages, distilled spirits such as whiskey,bourbon, vodka, scotch, and gin, petroleum distillates such as gasoline,diesel fuel, jet fuel, fuel oil and lubricating oil, propanediol,ethylene glycol, propylene glycol, lactic acid, acetic acid, citricacid, phosphoric acid, vegetable oil, glycerin, and wastewatereffluents.

[0035] The following list of contaminants are among those subject toremoval by the present method in the treatment of gas and vapor phasestreams: acetaldehyde, acetamide, acetone, acetonitrile, acrolein,acrylamide, acrylic acid, acrylonitrile, allyl chloride, ammonia,benzene, benzotrichloride, bromoform, 1,3-butadiene, butane, carbondisulfide, carbon tetrachloride, carbonyl sulfide, chlorine,chloroacetic acid, chlorobenzene, chloroform, chloroprene, o-cresol,m-cresol, p-cresol, cumene, cyclohexane, cyclohexanone, diazomethane,1,4-dichlorobenzene, 1,3-dichloropropene, diethanolamine,N,N-dimethylaniline, N,N-dimethylformamide, N,N-dimethylacetamide,1,1-dimethylhydrazine, dimethyl sulfate, 1,4-dioxane, epichlorohydrin,1,2-epoxybutane, ethyl acrylate, ethylbenzene, ethyl carbamate, ethylchloride, ethylene dibromide, ethylene dichloride, ethylene glycol,ethyleneimine, ethylene oxide, ethylene thiourea, ethylene dichloride,formaldehyde, gasoline vapor, hexachloroethane, hexane, hydrazine,hydrochloric acid, hydrogen fluoride, hydrogen sulfide, malodorcompounds, mercaptans, mercury, methanol, methyl bromide, methylchloride, methyl chloroform, methyl ethyl ketone, methyl hydrazine,methyl iodide, methyl isobutyl ketone, methyl methacrylate, methyltert-butyl ether, methylene chloride, N-methyl pyrrolidinone,naphthalene, nitrobenzene, phenol, phosgene, phosphine, propylenedichloride, propylene oxide, 1,2-propyleneimine, styrene, styrene oxide,sulfur dixoide, toluene, 1,2,4-trichlorobenzene, 1,1,2-trichloroethane,trichloroethylene, triethylamine, vinyl acetate, vinyl bromide, vinylchloride, vinylidene chloride, xylenes mixed isomers, o-xylene,m-xylene, p-xylene, and glycol ethers.

[0036] The following list of compounds are those which may be removed bythe present method from liquid fluid streams: alachlor, asbestos,atrazine, bad and/or objectionable taste and odor compounds, barium,benzene, cadmium, carbofuran, carbon tetrachloride, chlordane,chloramine, chlorine, chloroform, chlorobenzene, chromium-hexavalent,chromium-trivalent, color bodies, copper, 2,4-D, dibromochloroprane,o-dichlorobenzene, p-dichlorobenzene, 1,2-dichloroethane,1,1-dichloroethylene, cis-1,2-dichloro ethylene,trans-1,2-dichloroethylene, 1,2-dichloropropane, dinoseb, endrin,ethylbenzene, ethylene dibromide, fluoride, geosmin, heptachlor (H-34 orHeptox), heptachlor epoxide, hexachlorocyclopentadiene, lead, lindane,mercury, methoxychlor, methyl tert-butyl ether (MTBE), MIB, nitrate,nitrite, pentachlorophenol, polychlorinated biphenyls (PCBs), radon,selenium, simazine, styrene, 2,4,5-TP (silvex), tetrachloroethylene,toluene, toxaphene, 1,2,4-trichlorobenzene, 1,1,1-trichloroethane,1,1,2-trichloroethane, trichloroethylene, TTHM, xylenes mixed isomers,o-xylene, m-xylene, and p-xylene.

[0037] The following examples describe the method and properties ofmaterials that have been treated.

EXAMPLE 1

[0038] Two types of coatings were applied to pellets of WestvacoCorporation BAX 1100 activated carbon that provided dust free carbons: ahigh-density polyethylene (ChemCor polyethylene emulsion Poly Emulsion325N35) and aminoethylaminopropylpolysiloxane (General Electric siliconeemulsion SM2059). Other polymers, including polypropylene andpolystyrene, may be employed as alternative coating materials. Coatingproperties, such as abrasion resistance, permeability, and porosity, mayalso be further enhanced for a particular class of polymer by selectingmaterials with different molecular weight, density, particle size,and/or degree of cross-linking.

[0039] The activated carbon pellets were coated by tumbling in arotating cylinder and initially heated to 250° F. (121° C.) using a hotair gun. An emulsion of the polymer was then sprayed on the carbon insuccessive doses as the activated carbon was maintained at about 150° F.(66° C.) under the hot air flow. (The emulsion of the polyethylenesolution was 3.5 wt % solids. The emulsion of the polysiloxane solutionwas 3.9 wt % solids.) The coated activated carbon was then driedovernight at 220° F. (105° C.). After drying, any residual dust on thepellet exterior was removed by applying the vibration and airflowtreatment of the first 10-20 minutes of the dust attrition test(described below). The final coated product has a shiny, smoothappearance, compared with the (lull exterior of the uncoated material.

[0040] Table I compares the dusting attrition properties for theuncoated and coated pellets. Data for a baseline sample using onlyde-ionized water for the spray are also included to prove the importanceof the polymer coating on the change in dust properties. Dust attritionrates were measured with the two-point method in a 30-minute test(described below). TABLE I Coating Initial Dust Loading Dust Rate ADSample ID (wt %) (mg/dL) (mg/min/dL) (g/mL) Uncoated¹ 0.361 11.4 0.690.353 11.4 0.69 0.357 Polyethylene Emulsion Run 1A 2.9² 0.00 0.00 0.361Run 1B 1.6³ 0.00 0.00 0.356 Silicone 3.4⁴ 0.00 0.00 0.349 Emulsion Run 2

[0041] Initial dust and dust rate values were measured by a modified,3-filter version of the “Standard Test Method for Dusting Attrition ofGranular Carbon” (ASTM D5159-91). A 1.0 dL sample of carbon is placed ona screen with 0.250 mm openings in a test cell holder and is subjectedto vibration of 40 m/s/s RMS acceleration and downward air flow of 7L/min for a 10 minute interval. A glass fiber filter, placed below thesample screen, collects dust from the sample. The vibration and airflowstep is conducted three times with three different filters. The dustrate is calculated by the following equation:

Dust Rate (mg/min/dL), DR=0.0732 w ₃

[0042] where w₃ is the milligram weight gain of the third filter.

[0043] The dust rate from this equation is within a standard deviationof ±13% of the dust rate obtained by the standard ASTM procedure thatuses filter weight data from three additional 10 minute test intervals.

[0044] The initial dust is calculated as the milligram weight gain forthe first filter, w₁, minus the amount of dust attrited within 10minutes (10 ×DR):

Initial Dust (mg/dL)=w ₁−10 DR.

[0045] Note that the weight gain of the second filter, w₂, is notdirectly applied in these calculations. However, the w₂ value hasutility in confirming whether dust rate detection limits have beenreached for a sample by showing a zero or negative weight gain.

[0046] The inherent error in dust rate is ±0.01 mg/dL by a partialdifferential error analysis of its equation for calculation and the 0.1mg readability of the four decimal place gram balance required in theprocedure. Likewise, the inherent error in initial dust is ±0.3 mg/dL.Therefore, the non-detect dust rate value would be 0.01 mg/min/dL andthe initial dust value would be 0.3 mg/dL.

[0047] Compared with the reduction of initial dust, the sharp reductionin dust rate is the more important feature of the coated shaped orgranular activated carbon materials. By definition, a dust rate of 0.01μg/min/dL or less means that initial dust was removed within theattrition test to the detection limits of the test, and demonstratesthat initial dust would be likewise readily removed by other means.Alternatively, complete removal of initial dust without a sharpreduction in dust rate is perceived as being comparatively less usefulsince dust would be expected to readily reappear upon exposure of thesample to inter-particle motion from vibration, agitation or othermotive force acting thereon.

[0048] The data in Example 1 show that, as a result of the polymercoatings, the treated samples show initial dust and dust rate values inthe non-detect range.

EXAMPLE 2

[0049] Further tests show that similarly coated activated carbon pellets(Westvaco Corporation BAX 1500) exhibit increased abrasion resistance,as measured by a standard pellet hardness test (CTC Procedure 960-130),which is a modified version of ASTM D3802-79 (ball pan hardness). Thepellet hardness test involves shaking the sample (2 mm extruded carbonpellets) in a Ro-Tap Sieve Shaking Machine with stainless steel balls(10 of ¾ inch diameter and 20 of ½ inch diameter) and measuring theamount of pellet breakage in terms of the change in mean particle sizeof particles collected in a special pan at the bottom of an equivalent 6(full height) high sieve nest (consisting of #6, #8, #10, #12, #14, #18,and #60). Step 1: a standard sieve analysis is performed on 100 grams ofsample material and the fractions of material on each sieve is weighed.Step 2: then the fractions are combined in the special pan with the 30steel balls, and the special pan is shaken on the Ro-Tap for 20 minutes,after which the shaken sample is poured onto the top sieve of the sievenest. Repeat steps 1 and 2, except the Ro-Tap time for step 2 is 10minutes. Calculate the average particle size. The strength values aredetermined by dividing the mean particle diameter after grinding by theinitial mean particle diameter and multiplying the quotient by 100.

[0050] One coated sample (“Run 3A”) was as a composite of 10 replicatepreparations using the polymer application method of Example 1. Anothercoated sample (“Run 3B”) was prepared differently. A larger, 2-ftdiameter rotating cylinder with lifters was used, and the samples wereinitially heated by indirect- and direct-fired burners rather thandirect hot air flow. No de-dusting step was applied.

[0051] Table II compares the hardness, butane and dust attritionproperties for the uncoated and coated pellets. Dust data were measuredby a three-filter test method. TABLE II Coating Initial Sample LoadingPellet AD Dust Dust Rate ID (wt %) Hardness (g/mL) (mg/dL) (mg/min/dL)Uncoated — 68.6 0.295 3.2 0.22 Coated Run 3A 3.3 99.9 0.304 0.9 0.01 Run3B¹ 2.6 100.0 0.298 1.8 0.03

[0052]² Different preparation method vs. Run 3A, plus no de-dusting stepemployed to remove initial dust.

[0053] The demonstration of increased hardness was made with 2 mmdiameter BAX 1500 pellets of 68.6 hardness before coating. Pelletscoated with about 1-3 wt % polyethylene have hardnesses of 99.9-100.0,indicating no change in mean particle size in the test.

EXAMPLE 3

[0054] To show that the coating process of dust attrition reduction orelimination is applicable to a variety of commercial activated carbons,samples of a shaped commercial coal-based activated carbon (Kuraray 3GX)and a shaped commercial olive pit-based activated carbon pellets (NoritCNR 115) were coated with polyethylene (9.0 wt % emulsion solids) andcompared with a similarly coated shaped commercial wood-based activatedcarbon (Westvaco Corporation BAX 1500). The polymer coating has the samebenefits as previously shown with wood-based BAX 1100 and BAX 1500pellets for reducing dust without significant effect on key properties.

[0055] The coatings were applied by the previously described method ofExample 1. A de-dusting step was not applied prior to analyses. Thepolymer loadings (coating wt. %) were determined by heating samples to932° F. (500° C.) and measuring the amount of volatilized componentswith a hydrocarbon analyzer calibrated with carbons of knownpolyethylene content.

[0056] The results are shown in Table III and FIGS. 1, 2, and 3. TABLEIII Measured Initial Dust Loading AD Dust Rate Sample ID (wt %) (g/mL)(mg/dL) (mg/min/dL) 2 mm wood-based Uncoated* — 0.282 2.24 0.15 — 0.2833.31 0.11 average: 0.283 2.78 0.13 Coated Run 4A 0.4 0.279 1.42 0.06 Run4B 1.1 0.282 0.81 0.03 Run 4C 2.4 0.288 0.28 0.02 2.8 mm coal-basedUncoated* — 0.326 — 0.323 6.76 0.53 average: 0.325 6.76 0.53 Coated Run5A 0.7 0.328 3.00 0.00 Run 5B 1.5 0.334 0.70 0.00 Run 5C 2.8 0.337 0.000.00 2 mm olive pit-based Uncoated — 0.355 5.7 0.22 Coated Run 6A 0.70.347 1.24 0.04 Run 6B 1.4 0.353 0.23 0.01 Run 6C 2.4 0.356 1.60 0.00

[0057] Compared with their respective uncoated base carbons, initialdust and dust rate are sharply reduced.

EXAMPLE 4

[0058] Acrylic copolymer is another example of an active carbon coatingmaterial, in addition to the previously cited polyethylene and siliconematerials, in the present invention. BAX 1100 and BAX 1500 active carbonpellets were coated in the lab with JONREZ7 E-2062, an acrylic copolymersalt solution produced by Westvaco Corporation.

[0059] The coatings were applied by the previously described method ofExample 1. After evaluating the properties of two samples of uncoatedBAX 1500, two samples of the same BAX 1500 plant production were coatedwith a 9.0 wt % solids acrylic copolymer emulsion. Similarly, aftermeasuring the properties of a sample of uncoated BAX 1100, a sample ofthe same BAX 1100 plant production was coated with a 6.0 wt % solidsacrylic copolymer emulsion. A de-dusting step was not applied prior toanalyzing the coated products. The coating loading on BAX 1500 wasdetermined by heating samples to 932° F. (500° C.) and measuring theamount of volatilized components with a hydrocarbon analyzer calibratedwith carbons of known acrylic copolymer content. The coating loading onBAX 1100 was derived from the wet-basis weight gain of the coated sampleand the amount of applied emulsion spray. The acrylic copolymer coatinghas the same benefits as previously shown with polyethylene and siliconefor reducing dust, as shown in Table IV. TABLE IV Initial Dust CoatingAD Dust Rate Sample ID (wt %) (g/mL) (mg/dL) (mg/min/dL) Uncoated —0.282 2.24 0.15 BAX 1500¹ — 0.283 3.31 0.11 0.283 2.78 0.13 average:Coated with Acrylic Copolymer Run 7A 1.6² 0.277 1.93 0.01 Run 7B 3.4²0.283 1.30 0.00 Uncoated — 0.361 BAX 1100³ — 0.353 11.40 0.69 average:0.357 11.40 0.69 Coated with Acrylic 4.3⁴ 0.352 1.02 0.00 Copolymer Run8

[0060] The data show that a 1.6 wt % polymer coating on the BAX 1500shaped active carbon essentially eliminated dusting. Even moresurprising is that a 3.4 wt % coating on the same active carbon materialachieved total elimination of dusting. Also, a 4.3 wt % coating of theBAX 1100 shaped active carbon achieved a total elimination of dusting.

[0061] As the polyethylene coating on 10×20 mesh RGC was increased, theamount of dust that transferred from the carbon to water decreased from24.3 mg/dL to 0.5 mg/dL, as shown in FIG. 1. The concentration of dustin water was quantified by measuring the transmittance at a wavelengthof 440 nm with a spectrophotometer. A calibration between transmittanceand dust concentration was made using water slurries containing a knownconcentration of carbon fines. Carbon fines used were formed by spexmilling RGC for one minute. FIG. 3 data are listed in Table V. TABLE VColor, Composition, and Fines Properties of Coated Wood-based CarbonSamples Polyethylene Pigment Fines Carbon Pigment Content ContentContent Color Identification wt % wt % mg/dL Black(a) none 0 none 24.3Black none 0.5 none 16.3 Black none 1 none 7 Black none 2 none 3.2 Blacknone 4 none 1.2 Black none 6 none 0.5 Silver Afflair 119 Polar White (b)3.5 2 3.9 Blue-grey DuPont TI-Pure Titanium Dioxide 3.3 3 2.8Silver-grey Afflair 103 Rutile Silver (b) 1.8 1 10.7 Silver-grey Afflair111 Rutile Fine Silver 1.8 1 3.9 Gold Afflair 500 Bronze (b) 3.5 2.7 3.9Red Afflair 502 Red Bronze b 5 2.7 1.6, 3.2 Silver Afflair 119 PolarWhite (b), 6.8 5 3.9, 6.4 DuPont TI-Pure Titanium Dioxide Silver Afflair119 Polar White (b) 3.5 2.7 3.6 Yellow Afflair 351 Sunny Gold (b) 3.52.7 4.3 Red Afflair 502 Red Bronze (b) 3.5 2.7 11.3 Yellow Afflair 205Rutile Platinum Gold (b) 3.5 2.7 7.3 Green Afflair 235 Rutile Green (b)3.5 2.7 6.8 Purple Afflair 219 Rutile Lilac (b) 3.5 2.7 6.9 SilverAfflair 111 Rutile Fine Silver (b) 3.5 2.7 2.7

[0062] Uncoated wood-based activated carbon and the same carbonmaterials coated with 2% polyethylene had little to no difference inchlorine removal performance as shown in FIG. 4. The 2% coated carbonhad fines of 3.2 mg/dL, compared to the 24.3 mg/dL of the uncoatedcarbon. After each carbon treated 425 gallons of water, chlorine removalby the uncoated and coated carbon remained above 95%. Two columns, 12inches long and 1 inch in diameter containing 50 grams of 10×20 meshcarbon, were tested simultaneously at flow rates of 500 ml/min. Bleach(6% solution of sodium hypochlorite) was injected at a rate of 1 ml/hrinto deionized water to create a feed having about 1 ppm free chlorine.Deionized water was used to avoid forming chloramines, which resultswhen bleach is added to tap water containing nitrogen compounds.

[0063] Color change features could be incorporated into carbon coatingsto indicate when adsorptive capacity is spent so filters are used moreefficiently. Manufacturers' recommendations for changing POU filters areusually based on either a time period of use or a volume of watertreated. On-line monitoring of the effluent concentration of the filterrequires electronic components that are not economically suitable forPOU applications. With either the time or volumetric basis forchangeout, it is difficult for users to change their filters when theircapacity has been used to maximum benefit. When filters are changed withsome adsorptive capacity remaining, then users incur added expense. Whenfilters are changed after they are saturated, breakthrough one or morecomponents has likely occurred. Both cases of added expense andbreakthrough are undesirable to carbon filter users. A color-changingindicator that provides a more precise method identifying when filtersshould be replaced is therefore useful.

[0064] When a new carbon filter is put on-line, the concentration of acomponent targeted for adsorption will be low in the vicinity of theoriginal “fresh” coating since it will be adsorbed by the activatedcarbon. As the activated carbon becomes saturated at the feed end of thefilter, the concentration of the adsorbate in the water surrounding the“fresh” coating will increase. With a coating designed to undergo acolor change triggered by the increase in concentration, a second“spent” color will develop in the filter bed. The “spent” color willdevelop at the feed end and move towards the product end of the filter.For example, a pigment in the coating could become bleached by freechlorine present in municipal drinking water. The opposite could occuras well, as many colorless compounds exist that can be oxidized bychlorine into chromophores. The user would replace the filter when theentire length of the filter changed from the fresh to the spent color,confident that the filter's maximum useful life has been obtained.Either the “spent” or “fresh” color could be colorless or clear. Thecolor indicating compound could be added as a pigment to the coating oras a reactive chemical group grafted onto the coating polymer.

[0065] Thus, the subject matter of the applicants' invention is:

[0066] (1) A method for capturing chlorine from a fluid streamcontaining same by routing said stream through a filter comprising anactivated carbon material having its surface coated with a continuousfilm of a polymer, said polymer film being operable for essentiallyeliminating attrition of the activated carbon material resulting fromdusting;

[0067] (2) the method of (1) wherein the activated carbon material iscoated by:

[0068] (a) spraying an emulsion of the polymer onto exposed surfaces ofthe activated carbon material while it is in a state of turbulence at aprocessing temperature above ambient temperature; and

[0069] (b) drying the coated activated carbon material at above ambienttemperature.

[0070] While the preferred embodiments of the present invention havebeen described, it should be understood that various changes,adaptations, and modifications may be made thereto without departingfrom the spirit of the invention and the scope of the appended claims.It should be understood, therefore, that the invention is not to belimited to minor details of the illustrated invention shown in preferredembodiment and the figures and that variations in such minor detailswill be apparent to one skilled in the art. The claims, therefore, areto be accorded a range of equivalents commensurate in scope with theadvances made over the art.

What is claimed is:
 1. A method for capturing contaminants from a fluidstream containing same by routing said stream through a filtercomprising an activated carbon material having its surface coated with acontinuous film of a polymer, said polymer film being operable foressentially eliminating attrition of the activated carbon materialresulting from dusting.
 2. A method for capturing chlorine from a fluidstream containing same by routing said stream through a filter comprisedof a polymer-coated activated carbon prepared by coating the activatedcarbon material according to the steps of: (a) spraying an emulsion ofthe polymer onto exposed surfaces of the activated carbon material whileit is in a state of turbulence at a processing temperature above ambienttemperature; and (b) drying the coated activated carbon material atabove ambient temperature.
 3. The method of claim 2 comprising a furtherstep (c) de-dusting the dry coated activated carbon material by removingany residual dust therefrom.
 4. The method of claim 3 further comprisingan initial step of heating the active carbon material at above ambienttemperature.
 5. The method of claim 3 wherein the processing temperatureis maintained from 50° F. (10° C.) to 280° F. (138° C.) for from about 1minute to about 12 hours.
 6. The method of claim 5 wherein theprocessing temperature is maintained from about 70° F. (21° C.) to about250° C. (121° C.) for from about 5 minutes to about 6 hours.
 7. Themethod of claim 1 wherein the polymer is selected from the groupconsisting of.polyethylene, polypropylene, polyisobutylene, polystyrene,polyisoprene, polychloroprene, poly-4-methyl-1-pentene, polybutadiene,polybutene, polyacrylate, polymethyl methacrylate,polybutylmethacrylate, polymethacrylates, polyacrylic acid,polytetrafluoroethylene, trifluoroethylene, vinyl fluoride,fluorvinylidene, fluorobutylene, fluoropropylene, polyurethane,polyethylene terephthalate, styrene butadiene, modified polybutadiene,epoxies, modified alkyds, polyesters, starches, methyl cellulose, ethylcellulose, carboxymethyl cellulose, polyvinyl acetate, celluloseacetate, cellulose nitrate, cellulose triacetate, cellulose acetate,phthalate, cellulose propionate morpholinobutyrate, hydroxypropylmethylcellulose, ethylene vinyl acetate, acrylic polymers and copolymers,polysulfones, polyether sulfones, polyethers, polyethylene, glycols,polyimines, polybutylene, polyvinyl ethers, polyvinyl esters,polyalkylsulfides, polyarylsulfides, lignosulfonates, polyacrylamide,cyanoacrylate, polyamides, polyimides, polysiloxanes, methacrylonitrile,polyacrylonitrile, polyvinyl pyridine, polyvinyl benzene, polyvinylacetate, polyvinyl pyrrolidene, polyvinyl butyral, polyvinyl alcohol,polyvinyl chloride, polyvinyl formaldehyde, polyformaldehyde,polycarbonates, and polyvinylidene chloride.
 8. The method of claim 7wherein the polymer is selected from the group consisting of acrylicpolymer and polyethylene.
 9. The method of claim 1 wherein the activecarbon material is derived from a member of the group consisting ofcoal, lignocellulosic materials, petroleum, bone, and blood.
 10. Themethod of claim 9 wherein the lignocellulosic materials are selectedfrom the group consisting of including pulp, paper, residues from pulpproduction, wood chips, sawdust, wood flour, nut shell, kernel, andfruit pits.
 11. The method of claim 2 wherein the polymer is selectedfrom the group consisting of polyethylene, polypropylene,polyisobutylene, polystyrene, polyisoprene, polychloroprene,poly-4-methyl-1-pentene, polybutadiene, polybutene, polyacrylate,polymethyl methacrylate, polybutylmethacrylate, polymethacrylates,polyacrylic acid, polytetrafluoroethylene, trifluoroethylene, vinylfluoride, fluorvinylidene, fluorobutylene, fluoropropylene,polyurethane, polyethylene terephthalate, styrene butadiene, modifiedpolybutadiene, epoxies, modified alkyds, polyesters, starches, methylcellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl acetate,cellulose acetate, cellulose nitrate, cellulose triacetate, celluloseacetate, phthalate, cellulose propionate morpholinobutyrate,hydroxypropylmethyl cellulose, ethylene vinyl acetate, acrylic polymersand copolymers, polysulfones, polyether sulfones, polyethers,polyethylene, glycols, polyimines, polybutylene, polyvinyl ethers,polyvinyl esters, polyalkylsulfides, polyarylsulfides, lignosulfonates,polyacrylamide, cyanoacrylate, polyamides, polyimides, polysiloxanes,methacrylonitrile, polyacrylonitrile, polyvinyl pyridine, polyvinylbenzene, polyvinyl acetate, polyvinyl pyrrolidene, polyvinyl butyral,polyvinyl alcohol, polyvinyl chloride, polyvinyl formaldehyde,polyformaldehyde, polycarbonates, and polyvinylidene chloride.
 12. Themethod of claim 11 wherein the polymer is selected from the groupconsisting of polysiloxane, acrylic copolymer and polyethylene.
 13. Themethod of claim 1 wherein the active carbon material is derived from amember of the group consisting of coal, lignocellulosic materials,petroleum, bone, and blood.
 14. The method of claim 20 wherein thelignocellulosic materials are selected from the group consisting ofincluding pulp, paper, residues from pulp production, wood chips,sawdust, wood flour, nut shell, kernel, and fruit pits.
 15. The methodof claim 2 wherein a color pigment is added to the polymer emulsion toproduce a colored carbon material.
 16. The method of claim 1 wherein thefluid stream is selected from the group consisting of liquid streams andgaseous and vapor streams.
 17. The method of claim 16 wherein the fluidstream is liquid and the contaminants are selected from the groupconsisting of alachlor, asbestos, atrazine, bad and/or objectionabletaste and odor compounds, barium, benzene, cadmium, carbofuran, carbontetrachloride, chlordane, chloramine, chlorine, chloroform,chlorobenzene, chromium-hexavalent, chromium-trivalent, color bodies,copper, 2,4-D, dibromochloroprane, o-dichlorobenzene, p-dichlorobenzene,1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene,trans-1,2-dichloroethylene, 1,2-dichloropropane, dinoseb, endrin,ethylbenzene, ethylene dibromide, fluoride, geosmin, heptachlor (H-34 orHeptox), heptachlor epoxide, hexachlorocyclopentadiene, lead, lindane,mercury, methoxychlor, methyl tert-butyl ether (MTBE), MIB, nitrate,nitrite, pentachlorophenol, polychlorinated biphenyls (PCBs), radon,selenium, simazine, styrene, 2,4,5-TP (silvex), tetrachloroethylene,toluene, toxaphene, 1,2,4-trichlorobenzene, 1,1,1-trichloroethane,1,1,2-trichloroethane, trichloroethylene, TTHM, xylenes mixed isomers,o-xylene, m-xylene, and p-xylene.
 18. The method of claim 1 wherein thefluid stream is selected from the group consisting of gaseous and vaporstreams.
 19. The method of claim 18 wherein the fluid stream includesgaseous and vapor streams and the contaminants are selected from thegroup consisting of acetaldehyde, acetamide, acetone, acetonitrile,acrolein, acrylamide, acrylic acid, acrylonitrile, allyl chloride,ammonia, benzene, benzotrichloride, bromoform, 1,3-butadiene, butane,carbon disulfide, carbon tetrachloride, carbonyl sulfide, chlorine,chloroacetic acid, chlorobenzene, chloroform, chloroprene, o-cresol,m-cresol, p-cresol, cumene, cyclohexane, cyclohexanone, diazomethane,1,4-dichlorobenzene, 1,3-dichloropropene, diethanolamine,N,N-dimethylaniline, N,N-dimethyl formamide, N,N-dimethylacetamide,1,1-dimethylhydrazine, dimethyl sulfate, 1,4-dioxane, epichlorohydrin,1,2-epoxybutane, ethyl acrylate, ethylbenzene, ethyl carbamate, ethylchloride, ethylene dibromide, ethylene dichloride, ethylene glycol,ethyleneimine, ethylene oxide, ethylene thiourea, ethylene dichloride,formaldehyde, gasoline vapor, hexachloroethane, hexane, hydrazine,hydrochloric acid, hydrogen fluoride, hydrogen sulfide, malodorcompounds, mercaptans, mercury, methanol, methyl bromide, methylchloride, methyl chloroform, methyl ethyl ketone, methyl hydrazine,methyl iodide, methyl isobutyl ketone, methyl methacrylate, methyltert-butyl ether, methylene chloride, N-methyl pyrrolidinone,naphthalene, nitrobenzene, phenol, phosgene, phosphine, propylenedichloride, propylene oxide, 1,2-propyleneimine, styrene, styrene oxide,sulfur dixoide, toluene, 1,2,4-trichlorobenzene, 1,1,2-trichloroethane,trichloroethylene, triethylamine, vinyl acetate, vinyl bromide, vinylchloride, vinylidene chloride, xylenes mixed isomers, o-xylene,m-xylene, p-xylene, and glycol ethers.